Electrical insulating layers are typically required in both discrete semiconductor devices and in integrated circuits. This invention is concerned with a process for producing a local insulating layer by the oxidation of a semiconductor material.
The local oxidation of silicon (LOCOS) has been widely used for large scale integrated (LSI) circuits because it presents several advantages such as surface planarity, improvement in packing density and compatibility with standard LSI processing. However, the conventional LOCOS process used to produce a silicon dioxide insulating layer results in the formation of a so-called "bird's beak" shaped structure on the borders of the silicon dioxide. This phenomena reduces the width of non-insulated channels which are located between areas where the oxidation of silicon has occurred. This reduction in channel width is a major obstacle to the manufacturing of very large scale integrated (VLSI) circuits when devices are scaled down to the micrometer and submicrometer range. Thus, the fabrication of the bird's beak free device has been an essential objective for many future process and scaled device technologies.
Several prior art methods are known which purport to achieve the growing of thick oxide with small or even zero bird's beak structures, as shown in Isaac, "Fabrication Process for Full Box Isolation Without a Bird's Beak" IBM Technical Disclosure Bulletin, Vol. 22, No. 11 (April 1980) pp. 5148-51, Matsumoto, et at., "Method of Manufacturing Semiconductor Devices," U.S. Pat. No. 4,292,156 (Sept. 29, 1981) and Sun, et al., "Local Oxidation of a Semiconductor," U.S. Patent application Ser. No. 276,395 (filed June 6, 1981), now abandoned, but it has been observed that these methods are vulnerable to defect generation, particularly edge dislocations around the mesas or islands. These defects are directly related to and induced by the structures used in each method.